A reference manual for grain growers and advisers in the southern and western grains regions of Australia

In a winter cropping system, the return on investment from managing weeds in summer fallow (i.e. the period between crops) is high. Economic benefits flow from both extra amounts of high value water and nitrogen, crop establishment benefits and reduced issues with weed vectored disease and insect pests.

Stopping weed growth in the fallow can lead to yield increases in the following crop via several pathways. These include:

Increased plant available water

A wider and more reliable sowing window

Higher levels of plant available N

Reduced levels of weed vectored diseases and nematodes

Reduced levels of rust inoculum via interruption of the green bridge

Reduced levels of diseases vectored by aphids that build in numbers on summer weeds, and

Reduced weed physical impacts on crop establishment.

How farming country is managed in the months or years
before sowing can be more important in lifting water use
efﬁciency (WUE) than in-crop management. Of particularly
high impact are strategies that increase soil capture and
storage of fallow rainfall to improve crop reliability and yield.

Practices such as controlled trafﬁc farming and long term
no-till seek to change the very nature of soil structure to
improve inﬁltration rates and improve plant access to stored
water by removal of compaction zones.

Shorter term management decisions can have an equal
or even greater impact on how much plant available water
(PAW) is stored at sowing. These include decisions such as
crop sequence/rotation that dictate the length of the fallow
and amount of stubble cover, how effectively fallow weeds are
managed, stubble management and decisions to till/not to till
at critical times.

While many factors inﬂuence how much plant available
water is stored in a fallow period, good weed management
consistently has the greatest impact.